In a constant velocity universal joint to be used in a power transmission device of automobiles and various industrial machines, a main portion includes an outer joint member 210, a tripod member 220 serving as an inner joint member, and rollers 230 as illustrated in FIGS. 14 and 15. One shaft (drive shaft) of two shafts on a drive side and a driven side to be connected extends integrally from a bottom portion of the outer joint member 210, and the other shaft (not shown) thereof is connected to the tripod member 220.
The outer joint member 210 has a bottomed tubular shape having one end opened, and three track grooves 212 extending in an axial direction are formed on an inner circumference of the outer joint member 210 at equal intervals in a circumferential direction. The tripod member 220 includes three leg shafts 224 protruding from a cylindrical boss section 222 to outside in a radial direction, and the leg shafts 224 are inserted in the track grooves 212 of the outer joint member 210 to be engaged with the track grooves 212 to transmit torque. The roller 230 is rotatably fitted externally to each leg shaft 224 through intermediation of a needle-shaped roller 240, and rolling of the roller 230 along a pair of opposed roller guide surfaces 214 of the track groove 212 smoothens angular displacement and axial displacement between the two shafts to be connected.
An outer circumferential surface of the leg shaft 224 forms an inner rolling surface of the needle-shaped roller 240, and an inner circumferential surface of the roller 230 forms an outer rolling surface of the needle-shaped roller 240. A plurality of needle-shaped rollers 240 are provided between the outer circumferential surface of the leg shaft 224 and the inner circumferential surface of the roller 230 in a full roller state.
Each of those needle-shaped rollers 240 is held in contact with an inner washer 250 externally fitted to a root portion of the leg shaft 224 on an inner side in a radial direction, and is held in contact with an outer washer 260 externally fitted to a tip end portion of the leg shaft 224 on an outer side in a radial direction. The outer washer 260 is retained by fitting a retaining ring 270 such as a round circlip to an annular groove 226 formed in the tip end portion of the leg shaft 224.
Metal components such as the outer joint member of the constant velocity universal joint as described above is subjected to thermal hardening treatment for enhancing strength. As the thermal hardening treatment, there is given high-frequency heat treatment. In the high-frequency heat treatment, a coil suitable for each product in terms of a product shape, quenching depth, a quenching range, and the like is to be used.
As the related art, there is given a metal tube made of copper or the like to be used as a high-frequency induction heating coil (JP 2010-86904 A). Such a metal tube is assembled by brazing a plurality of components made of copper with silver solder or the like.
Specifically, a high-frequency induction heating coil for an outer joint member of a tripod type constant velocity universal joint, as illustrated in FIG. 14, and the like, is obtained by forming a plurality of components illustrated in FIG. 12 and brazing them for assembly.
In this case, a coil 10 includes heating sections 1a, 1b, and 1c to be fitted into three track grooves. The heating sections 1a, 1b, and 1c are hollow so that cooling water is allowed to flow therethrough. That is, the respective heating sections 1a, 1b, and 1c include heating section bodies 2 in an inverted U-shape, connecting members 3a, 3b, 3c, and 3d for connecting lower ends of the heating section bodies 2, cover members 4a, 4b, and 4c for closing openings of upper wall sections of the heating section bodies 2, cover members 5a, 5b, 5c, and 5d for closing lower openings of the connecting members 3a, 3b, 3c, and 3d, and inner flanges 6a, 6b, and 6c connected to the upper wall sections of the heating section bodies 2. Therefore, the coil 10 includes a total of 17 components.
Further, as illustrated in FIG. 19, a fixed type constant velocity universal joint generally includes an outer joint member 303 in which a plurality of guide grooves (track grooves) 302 are formed on an inner surface 301 thereof in an axial direction, an inner joint member 306 in which a plurality of guide grooves (track grooves) 305 are formed on an outer surface 304 thereof, a plurality of balls 307 disposed in ball tracks formed by the cooperation of the track grooves 302 of the outer joint member 303 and the track grooves 105 of the inner joint member 306, and a cage 308 having pockets 309 for accommodating the balls 307.
In this case, as illustrated in FIGS. 16 and 17, a hardened layer 310 is formed on the inner surface 301 of the outer joint member 303 by high-frequency heat treatment or the like.
A coil 320 to be used for the high-frequency heat treatment is assembled by, for example, brazing a plurality of components made of copper with silver solder. That is, as illustrated in FIG. 18, the coil includes components including first and second members 311, 312 for forming a current passage of a high-frequency current, a connector 313 for connecting the first and second members 311, 312, a first cover member 314 for closing an opening of the first member 311, and a second cover member 315 for closing an opening of the second member 312. In this case, the respective components are formed of copper or the like and are joined by brazing or the like.
In the coil, a cooling water passage through which cooling water flows is formed. That is, the cross-section of the coil is formed into a tubular shape for reducing the influence of self-heating and radiation heat from a heated product, and during use, cooling water is constantly passed through a tube (cooling water passage). However, the coil may be damaged by a stress generated by repeating self-heating or heating with radiation heat and cooling with the passage of cooling water.
Then, there have been proposed various methods as a coil life improving method. That is, heating time is extended by lowering an output, or a coil shape is devised as shown by JP 7-226292 A, JP 7-36395 A, etc.